more optimizations that v1 does and some cleanups

- a = a + x ==> a+=x
- joining consecutive var statements (hoisting is not always desirable)
- x == false ==> x == 0, x != true ==> x != 1
- x, x ==> x; x = exp(), x ==> x = exp()
- discarding useless break-s

lib/ast.js

@@ -70,7 +70,11 @@ function DEFNODE(type, props, methods, base) {
         ctor.prototype.TYPE = ctor.TYPE = type;
     }
     if (methods) for (i in methods) if (HOP(methods, i)) {
-        ctor.prototype[i] = methods[i];
+        if (/^\$/.test(i)) {
+            ctor[i.substr(1)] = methods[i];
+        } else {
+            ctor.prototype[i] = methods[i];
+        }
     }
     ctor.DEFMETHOD = function(name, method) {
         this.prototype[name] = method;
@@ -429,12 +433,45 @@ var AST_New = DEFNODE("New", null, {
     $documentation: "An object instantiation.  Derives from a function call since it has exactly the same properties."
 }, AST_Call);
 
-var AST_Seq = DEFNODE("Seq", "first second", {
+var AST_Seq = DEFNODE("Seq", "car cdr", {
     $documentation: "A sequence expression (two comma-separated expressions)",
+    $cons: function(x, y) {
+        var seq = new AST_Seq(x);
+        seq.car = x;
+        seq.cdr = y;
+        return seq;
+    },
+    $from_array: function(array) {
+        if (array.length == 0) return null;
+        if (array.length == 1) return array[0].clone();
+        var list = null;
+        for (var i = array.length; --i >= 0;) {
+            list = AST_Seq.cons(array[i], list);
+        }
+        var p = list;
+        while (p) {
+            if (p.cdr && !p.cdr.cdr) {
+                p.cdr = p.cdr.car;
+                break;
+            }
+            p = p.cdr;
+        }
+        return list;
+    },
+    add: function(node) {
+        var p = this;
+        while (p) {
+            if (!(p.cdr instanceof AST_Seq)) {
+                var cell = AST_Seq.cons(p.cdr, node);
+                return p.cdr = cell;
+            }
+            p = p.cdr;
+        }
+    },
     _walk: function(visitor) {
         return visitor._visit(this, function(){
-            this.first._walk(visitor);
-            this.second._walk(visitor);
+            this.car._walk(visitor);
+            if (this.cdr) this.cdr._walk(visitor);
         });
     }
 });
@@ -629,15 +666,19 @@ var AST_Undefined = DEFNODE("Undefined", null, {
     value: (function(){}())
 }, AST_Atom);
 
+var AST_Boolean = DEFNODE("Boolean", null, {
+    $documentation: "Base class for booleans",
+}, AST_Atom);
+
 var AST_False = DEFNODE("False", null, {
     $documentation: "The `false` atom",
     value: false
-}, AST_Atom);
+}, AST_Boolean);
 
 var AST_True = DEFNODE("True", null, {
     $documentation: "The `true` atom",
     value: true
-}, AST_Atom);
+}, AST_Boolean);
 
 /* -----[ TreeWalker ]----- */